Chunk rendering is extremely slow and random in 1.14

Creating new worlds with the official 1.14 or loading worlds in 1.13.2; 1.14 pre release 5, there is a slowdown in the loading of the chunks when we move (fly and elytra) in the world.
This problem did not occur before, in fact even the 1.14 pre-release 5 was much better than the official 1.14 released today 23 April 2019.
When you position yourself on an unloaded (invisible) chunk you can see that the blocks if selected with the pointer are there and you can even see their hitbox but as said before these are invisible.
I tried to optimize the worlds and press F3 + A but when I make the key combination the chuncks close to me immediately are loaded but those far away sometimes are never loaded remaining invisible.